1. Field of the Invention
The present invention relates to a photometer for reproduction machines, and more particularly to, a photometer for use in color reproduction machines suited to reproduce color documents having half tone, such as electrophotographic color reproduction machines, silver salt photographic color reproduction machines (optical printers) using reversal color paper, diffusion transferring photosensitive materials, etc., heat sensitive transferring color reproduction machines, ink jet color printers, and laser color printers, for example.
2. Description of the Related Art
While color reproduction machines have extensively been used in these days, they are required to finish the copy that is good not only in density but also in color balance. Photographs and prints are employed as color documents for such color reproduction machines in many cases, but the copied images of these documents will be different in color balance when copied under the same reproducing conditions, because of difference in color materials used and discrepancy between visual sensitivity and spectroscopic sensitivity of reproducing materials. For example, in color printed documents, the spectroscopic density profile of magenta ink is overlapped with that of cyan ink to a large extent. Therefore, when color reproduction machines are set to such reproducing conditions as suited to finish color printed documents with good quality, those reproducing conditions become less effective in developing the magenta density because the color printed documents have higher magenta density. Accordingly, if color photographic documents are copied under those reproducing conditions thus set, the copied color images would be deficient in magenta color and rich in green color.
In order to solve the foregoing problem, heretofore, different reproducing conditions (such as color filter adjusting amount, exposure amounts, charged amounts, development bias amounts) have been set in color reproduction machines dependent on color photographic documents and color printed documents. Then, operators touch the selection keys at their own discretion to select the reproducing conditions suitable for the type of color documents to be copied.
However, the type of color documents is judged based on the experience of individual operators, so it is difficult for those operators having no expert knowledge to correctly discriminate between color photographs and color prints produced therefrom, because of recent rapid advance of color printing technology.
For the reason, it has been proposed to discriminate between color photographs and color prints by previously making a photometric test (pre-scan) on the color document before it is copied. Such a preparatory photometric test on a color document is carried out by moving the color document and a slit relative to each other for scanning, and condensing the light reflected from the color document onto a detection sensor. The detection sensor has respective spectroscopic sensitivity corresponding to three primary colors in the color document, and the density values of three primary colors obtained by the detection sensor are employed to judge whether the color document is a color photograph or a color print.
However, where a color document has different colors on opposite sides of the intermediate portion of a slit along its length, the type of the color documents may not be judged correctly dependent on arrangement of the detection sensor. For example, when colors of a color document 11 are different in opposite sides of the intermediate portion of a slit 58 along its length, as shown in FIG. 12, i.e., when color of an area A in FIG. 12 is different from that of an area B, the type of the color document may not be determined correctly dependent on arrangement of the detection sensor.